With the increasing bandwidth requirements caused by the increase in people's demand for voice, data, multimedia, and other services, the OTN has gradually become a core platform for bearer services of various operators. Transmission of 40 Gigabit (40 G) Ethernet service data on the OTN is currently considered a hot topic.
FIG. 1 is a schematic structural view of an OTN frame. As shown in FIG. 1, the OTN frame includes an Optical Channel Payload Unit-k (OPUk) payload, an Optical Channel Transport Unit-k (OTUk) Forward Error Correction (FEC), and the following overhead (OH) portion caused by transmitting the payload:
OPUk OH; optical channel data unit-k (ODUk) OH; and OTUk OH.
FIG. 2 is a schematic view of an OH structure of the OTN frame shown in FIG. 1. Referring to FIG. 2, a client specific portion is set at positions corresponding to 15th and 16th bytes. The portion contains a payload structure identifier (PSI) occupying one byte.
OPU types and capacity corresponding to the OPUk are as shown in Table 1.
TABLE 1OPU Payload bitOPU TypeOPU Payload nominal bit raterate toleranceOPU12 488 320 kbit/s±20 ppmOPU2238/237 × 9 953 280 kbit/sOPU3238/236 × 39 813 120 kbit/sOPU1-XvX * 2 488 320 kbit/s±20 ppmOPU2-XvX * 238/237 * 9 953 280 kbit/sOPU3-XvX * 238/236 * 39 813 120 kbit/sNOTEThe nominal OPUk Payload rates are approximately: 2 488 320.000 kbit/s (OPU1 Payload), 9 995 276.962 kbit/s (OPU2 Payload) and 40 150 519.322 kbit/s (OPU3 Payload). The nominal OPUk-Xv Payload rates are approximately: X*2 488 320.000 kbit/s (OPU1-Xv Payload), X*9 995 276.962 kbit/s (OPU2-Xv Payload) and X*40 150 519.322 kbit/s (OPU3-Xv Payload).
It can be seen that, the payload bandwidth of the OPU3 is 40.150519322 GBits/s, which is slightly higher than 40 GBits/s. Considering a clock offset of −20 ppm in the OTN, the minimum payload rate of the OPU3 is 40.150519322 GBits/s*0.999980=40.149716311 GBits/s.
Currently, it is suggested that 40 G Ethernet service data be encoded through a 64/66B encoding scheme, and that the encoding rate required by the physical (PHY) layer for transmitting code blocks be 66/64*40 GBits/s=41.25 GBits/s.
Since the payload bandwidth of the OPU3 is smaller than the encoding rate required by the 40 G Ethernet PHY layer, 40 G Ethernet service data cannot be directly borne by the OPU3, and the encoding rate of 40 G Ethernet code blocks needs to be reduced to be lower than the minimum payload bandwidth of the OPU3.
Although the payload bandwidth requirements for transmission of the 40 G Ethernet code blocks in the OTN can be met after the encoding rate of the 40 G Ethernet code blocks is reduced to be lower than the minimum payload bandwidth of the OPU3, no specific solution for mapping the 40 G Ethernet code blocks to the OTN is provided currently.